alchemy

a medieval science aimed at the transmutation of metals, especially base metals, into gold
[Princeton Review]

medieval form of chemistry, the chief aim of which was to discover how to turn ordinary metals into gold [Barron]

a medieval chemical science and speculative philosophy aiming to achieve the transmutation of the base metals into gold, the discovery of a universal cure for disease, and the discovery of a means of indefinitely prolonging life [Taisha]